With the intelligent development of communication devices, people use smart terminals more and more frequently in daily lives, and a variety of activities such as video communication, calling, voice communication, music listening, video playback, and the like can be carried out by using the smart terminal. As a tool for transmitting sound, headphones bring better listening experience to the people and are widely used in people's daily lives. A user can use the headphone to listen to music, make calls, conduct voice or video communication, and play video. In more and more occasions, people like to wear headphones. Furthermore, the effects of sound insulation and noise reduction of the headphones are getting better and better.
When a user wears a headphone to listen to sound played by a terminal device, hearing of the user, which can assist visual sense, is greatly restricted by the sound played by the headphone. The user is hard to notice sound signals of external environment, which may cause missing some important information such as contents of other's speech. Therefore, the user may have to take off the headphone or pause the headphone to receive external sound, which may affect the user experience.